# CVE-2021-41866: Cross-site scripting in n/a

> Attackers can inject malicious scripts via unescaped template names in the admin panel, potentially compromising administrator accounts.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 26 Oct 2021
- **Updated:** 4 Aug 2024

## What is CVE-2021-41866?

CVE-2021-41866 is a medium-severity cross-site scripting vulnerability in Mybb Mybb, published on 26 Oct 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

MyBB before 1.8.28 allows stored XSS because the displayed Template Name value in the Admin CP's theme management is not escaped properly.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-41866?

It affects 1 product.


Products: Mybb Mybb.

## How do I fix CVE-2021-41866?

No fix has been published for CVE-2021-41866 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-41866 being exploited?

There is no known exploitation of CVE-2021-41866 in the wild and no public exploit code.

## Other vulnerabilities in Mybb Mybb

- [CVE-2011-10018](https://insights.sbomify.com/CVE-2011-10018/): myBB 1.6.4 Backdoor Arbitrary Command Execution (critical 10.0)
- [CVE-2015-2786](https://insights.sbomify.com/CVE-2015-2786/): Information disclosure in n/a (critical 10.0)
- [CVE-2011-5133](https://insights.sbomify.com/CVE-2011-5133/): Cross-site scripting in n/a (critical 10.0)
- [CVE-2006-0218](https://insights.sbomify.com/CVE-2006-0218/): SQL injection in n/a (critical 10.0)
- [CVE-2020-22612](https://insights.sbomify.com/CVE-2020-22612/): Code injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-41866 and fix it if it is affected.

What it is: CVE-2021-41866 is a medium-severity cross-site scripting vulnerability in Mybb Mybb, published on 26 Oct 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-41866 in the wild and no public exploit code.

Affected product: Mybb Mybb. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-41866/ (Markdown: https://insights.sbomify.com/CVE-2021-41866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-41866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-41866
- OSV: https://osv.dev/vulnerability/CVE-2021-41866

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-41866/
Summaries are generated and may contain mistakes; the official description above is the record.